Current evidence suggests that protein phosphorylation and dephosphorylation is an important mechanism in the control of cardiac function and metabolism. The phosphorylation states of a number of proteins important in regulating cardiac contractility change in response to a number of drugs and neurotransmitters (inotropic agents) which alter the contractile activity of cardiac muscle. The phosphorylation states of these proteins are regulated by the opposing actions of protein kinases and protein phosphatases. Although considerable work has been done on the protein kinases, very little is known about the cadiac protein phosphatases and their roles in regulating cardiac function. The proposed studies involve analysis of cardiac phosphatases and their functions in dephosphorylating proteins involved in contraction. This analysis is of fundamental importance for a more complete understanding of the control of phosphorylation states of cardiac proteins. The aims of these studies are to determine the number, substrate specificities, and native structures of bovine cardiac protein phosphatases. This will be accomplished using a combination of biochemical and immunological methods. Individual protein phosphatases will be prepared from bovine cardiac muscle. The specificities of the cardiac protein phosphatases will be determined toward a number of cardiac proteins including the inhibitory subunit of troponin, myosin light chains, myofibrillar C-protein, and proteins of the sarcoplasmic reticulum and sarcolemma. The protein phosphatases will also be used for the production of both monoclonal and polyclonal antibodies. These antibodies will then be used as probes for individual enzymes to determine the number of cardiac protein phosphatases, the native structures of these enzymes, and the possible structural relationships between different forms of the phosphatases.